Just a bought a new My Book Live 3tb, there is no Twonky server pre-installed. I have tried following a couple of the guides but keep getting hamstrung by the following error message when trying to unzip the file:

"End-of-central-directory signature not found. Either this file is not
a zipfile, or it constitutes one disk of a multi-part archive. In the
latter case the central directory and zipfile comment will be found on
the last disk(s) of this archive."

All the guides I have seen seem to be for upgrading from version 5 or 6. So I am not sure if these apply to my specific problem or not.

If this is serious "I R NooB" error then please forgive me and show me how to get things working?

I have a same problem. I have My book live 2tb over a year, yesterday I decided to buy another one (but 3tb version) to expand my storage space. After instaling and copying some videos I find out theres no Twonky, only WDs DLNA server, which is not so good and different. So I started to search how to revert back to a twonky. BUT, as you can see there is no way to switch back to twonky if you have a new version of my book live.
Support of WD says that.

Supported My Book Live Firmware:
The patches to switch Media Servers will only work if the following conditions are met:

The My Book Live already has Twonky Media Server.
Is running firmware version 02.41.05-034 and later.